Dipeptididyl peptidase-IV (Hereinafter, referred to as DPP-IV) is an enzyme that is generally identified as EC 3.4.14.5 by enzyme classification, functionally belongs to serine protease (Barrett A. J. et al, Arch. Biochem. Biophys., 1995, 247-250), and cleaves the N-terminal dipeptide from peptides that begin with the sequence H-Xaa-Pro-Y (or H-Xaa-Ala-Y wherein Xaa represents any lipophilic amino acid, Pro represents proline, and Ala represents alanine) (Heins J., et al., Biochim. et Biophys. Acta 1988, 161), and is also known as DP-IV, DP-4, or DAP-IV. The enzyme is widely distributed and found in a variety of mammalian tissues such as kidney, liver and small intestine (Hegen M. et al., J. Immunol., 1990, 2908-2914). DPP-IV was first identified as a membrane-bound protein. More recently, a soluble form thereof has been identified (Duke-Cohan J. S. et al., J. Biol. Chem., 1995, 14107-14114). According to studies and reports that have been recently published, it was revealed that such a soluble form of DPP-IV has the same structure and function as a membrane-bound form of the enzyme and is found without a certain membrane-bound domain in blood (Christine D. et. al, Eur. J. Biochem., 2000, 5608-5613).
Initial interest in DPP-IV has focused on its role in the activation of T lymphocytes. DPP-IV responsible for the activation of T lymphocytes was specifically designated as CD26. With the report showing that CD26 binds to or interacts with human immunodeficiency virus (HIV) (Guteil W. G. et al, Proc. Natl. Acad. Sci., 1994, 6594-6598), it was proposed that DPP-IV inhibitors could be useful in the treatment of AIDS (Doreen M. A. et al., Bioorg. Med. Chem. Lett., 1996, 2745-2748).
In addition to a critical role participating in the immune system, the main function of DPP-IV stems from its peptidolytic activity as described above. Attention was particularly given to the role of DPP-IV as it is found that DPP-IV is a key enzyme implicated in the degradation of glucagon-like protein-1 (hereinafter, referred to as “GLP-1”) in the small intestine (Mentlein R. et al., Eur. J. Biochem., 1993, 829-835). GLP-1 is a 30 amino-acid peptide hormone which is secreted by intestinal L cells as a response to food intake of the small intestine (Goke R. et. al, J. Biol. Chem., 1993, 19650-19655). Since this hormone is known to have potentiating effects on the action of insulin in the control of postprandial blood glucose levels (Hoist J. J. et al., Diabetes Care, 1996, 580-586), it was postulated that DPP-IV inhibitors might also be usefully employed in the treatment of type 2 diabetes. Based on this assumption, an early form of the DPP-IV inhibitor was developed with some reports demonstrating the therapeutic effectiveness of a medicine in animal experiments (Pauly R. P. et al., Metabolism, 1999, 385-389). Further, DPP-IV-deficient mice or rats maintained GLP-1 activity and high insulin levels, resulting in decreased blood glucose levels and such a genetic disruption or mutation of the DPP-IV gene exhibited no significant effect on the survival of individual animals (Marguet D. et al., Proc. Natl. Acad. Sci., 2000, 6874-6879). As a consequence, it was proposed that DPP-IV is feasible as a potent therapeutic agent for the treatment of type 2 diabetes, which resulted in accelerated research and development of the DPP-IV inhibitor.
Binding of GLP-1 with a receptor in a variety of tissues results in satiety (feelings of fullness), delayed gastric emptying, and facilitated growth of pancreatic beta-cells. Therefore, clinical trials for the treatment of the type 2 diabetes as described above are gradually increasing through intravenous administration of GLP-1 per se (Verdich C. et al, J. Clin. Endocrinol. Metab., 2001, 4382-4389). An in vivo half-life of GLP-1 is merely 2 min (Kieffer T. J., et al., Endocrinology, 1995, 3585-3596), so such a short half-life is a major obstacle to direct use of GLP-1 as a therapeutic agent. Since then, numerous research groups and institutions have made many attempts toward derivatization of GLP-1, resulting in development and commercialization of a peptide which is capable of protracting the short in vivo half-life (Deacon C. F., Diabetes, 2004, 2181-2189). However, such a GLP-1 derivative still suffers from a fundamental limitation in that it is an injectable formulation. Further, a great deal of interest has been increasingly focused on development of an efficient DPP-IV inhibitor, due to the fact that active GLP-1 (7-36) is degraded by DPP-IV and then converted into inactive GLP-1 (9-36) only within a short period of time, e.g. 2 min.
The beginning in the development of DPP-IV inhibitors was similar to the development trend of other inhibitors. That is, most of the research results were for substrate analogues. A representative one of these substrate analogues is a dipeptide derivative which was obtained as the product of the early research which was performed on a parent nucleus having a structure similar to that of Proline (Pro), based on the fact that DPP-IV exhibits pronounced affinity for a peptide containing a certain amino acid Proline (Chinnaswamy T. et al, J. Biol. Chem., 1990, 1476-1483). Typical examples of Proline-like structures include pyrrolidide and thiazolidide, and derivatives containing these parent nucleus compounds exhibit reversible and competitive inhibitory activity for the DPP-IV enzyme (Augustyns K J L., et al, Eur. J. Med. Chem., 1997, 301-309). Among products of such extensive research and development, there are continuing experiments on the action mechanism and efficacy of certain compounds, specifically Val-Pyr (Valine-Pyrrolidide), Ile-Thia (Isoleucine-Thiazolidide), and the like. Particularly, a great deal of attention has been focused on Ile-Thia, because the Val-Pyr structure exhibited relatively poor inhibitory activity on DPP-IV (Hanne B. R., et al, Nat. Struct. Biol., 2003, 19-25), which as such prompted intensive research and study on derivatives of the Ile-Thia compound.
Out of the derivative compounds focused and obtained by the above-mentioned research and study, a compound having the most prominent activity was beta-amino acid thiazolidide series which was attempted to be developed by Merck & Co., Inc. However, according to the results of pharmacodynamic and pharmacokinetic experiments performed in rats, the obtained compound exhibited significantly low bioavailability in conjunction with an apparent limitation in the inhibition of enzymatic activity (Jinyou Xu, et al, Bioorg. Med. Chem. Lett., 2004, 4759-4762). As a consequence, further development on compounds of this series was discontinued due to profound disadvantages.
During the above-mentioned investigation, Merck noticed that a beta-amino acid, in addition to a thiazolidide parent nucleus, is also a key factor having significant effects on the DPP-IV inhibitory activity. This finding was applied to the approach for substitution of the thiazolidide parent nucleus with a different parent nucleus compound (Linda L. B., et al, Bioorg. Med. Chem. Lett., 2004, 4763-4766). With such a subsequent research, a variety of derivatives having substitution of the thiazolidide parent nucleus with a piperazine parent nucleus were synthesized with drug efficacy testing and pharmacodynamic studies. Unfortunately, the piperazine derivatives of Merck still suffered from significantly poor bioavailability. According to the compound optimization to cope with such a disadvantage, sitagliptin, the product MK-0431 (trade name: JANUVIA), was developed with modification of a piperazine moiety to a triazolopiperazine moiety. This product is now commercially available under new drug approval by US FDA in 2006.

Thus, the present inventors discovered that when a substitution including a hetero atom is made on a piperazinone moiety, the thus-modified compound not only has excellent DPP-IV inhibitory activity, but also is capable of achieving significantly improved bioavailability as compared to conventional DPP-IV inhibitors, then succeeded in synthesis of a novel heterocyclic compound containing a beta-amino group, and completed an invention of a compound represented by the following Formula 1. Based on this, its application was filed as Korea Patent Application No. 2007-0038462.

(In formula 1, X is OR1, SR1, or NR1R2, wherein R1 and R2 are independently a C1˜C5 lower alkyl, or R1 and R2 of NR1R2 may form a 5-membered to 7-membered ring containing a hetero element of O.)
In addition to DPP-IV inhibitors which are currently under active development, diabetes or obesity therapeutic agents which are clinically used or under development include α-glucosidase inhibitors, Biguanides, insulin secretagogues, insulin sensitizers, cannabinoid receptor-1 antagonists, and the like.
α-glucosidase inhibitors exhibit the action of delaying the absorption of carbohydrate from the small intestine and include acarbose, voglibose, emiglitate, miglitol, and the like. Examples of biguanides include metformin, phenformin, or buformin. Insulin secretagogues may be divided into sulfonylurea and non-sulfonylurea species. Examples of sulfonylurea species include glybenclamide (glyburide), glipizide, gliclazide, glimepiride, tolazamide, tolbutamide, acetohexamide, carbutamide, chlorpropamide, glibornuride, gliquidone, glisentide, glisolamide, glisoxepide, glyclopyamide, glycylamide, glipentide, and the like. Examples of non-sulfonylurea species include repaglinide, nateglinide, and the like.
Metformin, a representative Biguanide, is a hypoglycemic agent that regulates high blood glucose levels without stimulating insulin secretion from the pancreas, and is advantageous in that it the drug may be applied to obese diabetic patients because metformin is not associated with weight gain and applied also to patients which are not susceptible to sulfonylurea drugs due to its different action mechanism. Although the action mechanism of metformin is not clearly known, the drug only reduces blood glucose levels of diabetic patients without affecting blood glucose levels of normal subjects, and does not have any action of stimulating β-cells in the pancreas to stimulate insulin secretion compared to sulfonylurea drugs. It is known that metformin increases the action of insulin in peripheral cells, such as liver and muscles and decreases glucose production from the liver, and it was reported in some studies that metformin acts in skeletal muscles and increases the movement of glucose through a cell membrane. In addition, the drug is characterized by improving dyslipidemia to lower blood LDL-cholesterol and triglyceride levels. Clinically, metformin may be administered in a relatively high dose, up to 200 mg per day, and twice a day, for example, morning and evening. When metformin is administered in excess of 2000 mg, it is administered with meal three times a day and the maximum dose per day is 2500 mg.
When metformin is applied to overweight diabetic patients, it is evaluated as an excellent diabetes therapeutic agent. However, care should be taken because adverse side effects may be accompanied by gastrointestinal system disorders, such as diarrhea, nausea, vomiting, and the like, blood system disorders, such as Vitamin B12 deficiency and the like, lactic acidosis which is a severe metabolic complication that is scarce but may lead to 50% mortality by internal accumulation of metformin, and the like.
Insulin sensitizers are relatively recently developed drugs, have a thazolidin-dione (TZD) structure, and act on peroxisome prolierator-activated receptors (PPARs). Examples of insulin sensitizers include troglitazone, ciglitazone, rosiglitazone (AVNADIA), pioglitazone (ACTOS), englitazone, and the like. Besides them, various studies are underway.
Cannabinoid receptor-1 antagonists are relatively recently developed drug targets, inhibit excessive activity of endocannabinoid to regulate the balance of body weight and energy as well as glucose and lipid metabolism, and act on cannabinoid receptor-1 (CB1 receptor) present in central and peripheral nervous systems.
Examples of cannabinoid receptor-1 antagonists include Rimonabant (ACOMPLIA), Otenabant, Ibinabant, Surinabant, and the like. Besides them, various studies are underway.
However, because diabetes or obesity is a chronic disease and its conditions are complicated, there are many cases in which symptoms of the disease are in progress, accompanied by various complications. Therefore, it is necessary to choose a medication most appropriate for the individual patient's conditions. When individual medications are administered alone, there are cases in which sufficient effects may be obtained according to its symptoms. In addition, there are many cases in which it is difficult in clinical practice to choose a medication due to many problems such as increase in dose or occurrence of adverse side effects resulting from prolonged administration. Thus, instead of methods for administering a single drug, various methods for administering one or more drugs with different mechanisms in combination have been recently suggested.
In particular, studies on literatures of combined administration of DPP-IV inhibitors and conventional diabetes therapeutic agents show that a pharmaceutical composition prepared by mixing 3˜20% (w/w) of sitagliptin, 25˜94% (w/w) of metformin, 0.1˜10% (w/w) of a lubricant, and 0˜35% (w/w) of a binder is disclosed. In the case of vidagliptin which is a compound commercially available as a trade name of Galvus from Novartis, combined pills of vildagliptin and metformin at ratios of 50˜98%, 60˜98%, 70˜98%, or 80˜98% are disclosed in International Publication Gazette WO 07/078,726, and combined pills of vidagliptin and pioglitazone, a PPAR agonist, by direct compression method are described in International Publication Gazette WO 06/135693. However, these literatures describe pharmaceutically optimal composition ratios in a preparation including a DPP-IV inhibitor and metformin or a PPAR agonist, rather than synergistic effects of the two drugs.
In addition, it is described in JPET (2004), 310, 614-619 that a DPP-IV inhibitor valine-pyrrolidide (val-pyr), when administered to an animal in combination with metformin, increased glucagon-like protein levels, decreased food intake and weight gain, and synergistically improved glucose tolerance.
It is disclosed in Life Science (2007), 81, 72-79 that combined administration of vildagliptin and rosiglitazone brought about significant improvement in serum glucose, triglyceride, and glucose tolerances, and pre-existing adverse side effects such as edema from rosiglitazone and the like were alleviated by combined administration of vildagliptin.
It is identified in International Publication Gazette WO 04/052362 that as a result of a glucose tolerance test on vildagliptin and a PPAR agonist micronized fenofibrate, the area under curve (AUC) was decreased by 18% with a single administration of vildagliptin and by 7% with a single administration of fenofibrate while the AUC was decreased by 33%, insulin sensitivity was improved, and weight gain was reduced with a combined administration of the two drugs.
It is mentioned in J. Pharmacol Sci. (2007), 104, 29-38 that postprandial high blood glucose levels are effectively decreased with a combined administration of E3024 which is a DPP-IV inhibitor, voglibose which is an α-glucosidase inhibitor, and acarbose, and in JPET (2007), 320(2), 738-746 that when E3024 is administered in combination with glybenclamide or nateglinide, which is a kind of insulin secretagogue, postprandial high glucose levels are also effectively decreased.
It is mentioned in Korea Patent Publication No. 2003-0019440 that when a compound described in International Publication Gazette WO 99/061431 is administered in combination with a conventional diabetes therapeutic agent, the plasma DPP-IV activity, hemoglobin concentration (HbAlC, %), and plasma glucose are significantly reduced.
It is described in International Publication Gazette WO 07/074,884 that when alogliptin is administered in combination with voglibose, pioglitazone, and the like, pancreas protective effects are enhanced.
It is mentioned in International Publication Gazette WO 07/006,769 that vildagliptin and rimonabant, which are cannabinoid receptor-1 antagonists, are administered in combination, blood glucose and lipid levels and weight are effectively improved, and described in WO 06/119260 that when sitagliptin and a cannabinoid receptor-1 antagonist are administered in combination, glucose tolerance and insulin resistance are improved.
Thus, the present inventors have developed a compound of Formula 1, which is a novel DPP-IV inhibitor, discovered that when the compound is administered in combination with an antidiabetic or antiobesity agent, an excellent glucose tolerance is exhibited, blood glucose levels are effectively inhibited, and fat mass is reduced, thereby leading to completion of the present invention.